Copyright is a form of protection provided by the laws of the United States to the authors of "original works of authorship (not copied) which are fixed in any tangible medium expression." Article 1, Section 8 of the U.S. Constitution represents our founding fathers effort, "To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries."
Musical works: this generally refers to musical scores and accompanying words
Dramatic works: plays, films, radio, television scripts
Pantomimes and choreography
Pictorial, graphic and sculptural works
Motion pictures and other audiovisual work (film, television show, videogame, etc.)
Sound recording: performance of musical works, audio recordings of literary works
Architectural works: just the designs, not the building itself.
Data is not protected but your expression of data is.
Facts: no one may claim originality as to facts.
Works in the public domain, which include:
Works whose copyright has expired before 1923.
Works created by the U.S. Government or a U.S. Government entity.
Directions, recipes or concoctions: however this may be covered under trade secret law or a patent.
Works that are not fixed (fixed describes anything created, documented or recorded in some way):
Choreography developed during a dance class that wasn't recorded.
Music played during a jam session that wasn't recorded.
Names, phrases, slogans, titles and symbols: but again, these could be protected under trademark.
Variations of typographic ornamentation, lettering or coloring.
Simple listings: table of contents, recipe ingredients: however you can be protected by copyright by the way facts have been ordered.
Procedures, methods and processes.
Works consisting of common facts such as a ruler, a calendar or a height/weight chart.
(these images were accessed through Google's 'available for reuse' search tool)
Textbooks
Nonfiction sources
Scholarly articles
But you may be able to secure copyright for your arrangement of facts/data
A section of facts and data used in an annotated bibliography
Arrangement or layout of a pie chart or graph
Copyright in a new expression/components of public domain works. For example:
The book The Three Musketeers is no longer protected under copyright (published prior to 1923), but if Barnes & Noble decides to print a copy with a new introduction, that introduction is copyright protected. The same goes for the recreation of The Three Musketeers into a movie, the movie is then copyrightable.
Works created by employees of U.S. Government could have copyrightable components.
Copyright in Graphic Design
Bringing shapes, lettering and coloring together in a way that is protected under law.
Copyright in instructions
Copyright in listings/arrangements of facts.
(this image was accessed through Google's 'available for reuse' search tool)